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Pulmonic stenosis is common in dogs and infrequent in cats. It results in obstruction to right ventricular outflow due, in most cases, to dysplasia of the pulmonic valve cusps. The stenosis can also occur in the infundibulum, the subvalvular region, or in the supravalvular area. |
| Pathophysiology: |
| The right ventricle must generate increased pressure during systole to overcome the stenosis, which in moderate to severe cases can lead to dramatic right ventricular hypertrophy and dilatation. As the right ventricle hypertrophies, ventricular compliance diminishes, leading to increased right atrial pressure and venous congestion. The increased flow velocity deforms the wall of the main pulmonary artery, resulting in a poststenotic dilatation. In severe cases, right-sided
congestive failure may be noted. Supravalvular pulmonic stenosis is uncommon and may be most often observed in Giant Schnauzers. Concurrent tricuspid valve dysplasia is sometimes noted in animals with pulmonic stenosis. Anomalous coronary artery development has been documented in some affected animals with pulmonic stenosis such as Boxers and English Bulldogs. Typically, the left main coronary artery originates from a single right coronary artery and encircles the right
ventricular outflow tract. |
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| Clinical Findings and Treatment: |
| Affected animals may have a history of failure to thrive and exercise intolerance. Right-sided CHF may be present and is characterized by ascites or peripheral edema. A prominent ejection-type systolic murmur is present and heard best at the pulmonic valve area. A corresponding precordial thrill is usually present. Jugular distention and pulsations may also be present. Electrocardiography will demonstrate evidence of right ventricular enlargement in many cases. Radiographic
abnormalities include right ventricular enlargement, an aneurysmal dilatation of the main pulmonary artery, and diminished pulmonary perfusion. Echocardiography is indicated in these cases and may demonstrate right ventricular dilatation and hypertrophy, interventricular septal flattening, and thickened and relatively immobile pulmonic valve cusps. In a few cases, supravalvular or discrete subvalvular stenosis can be noted. Pulmonic insufficiency can sometimes be noted in dogs
with pulmonic stenosis. Doppler evaluation is valuable in determining the severity of the stenosis. Based on severity (reported as the pressure gradient across the valve), the need for intervention can be assessed. Animals with moderate or severe pulmonic stenosis can benefit from balloon valvuloplasty or surgical intervention (valvulotomy, patch grafting, partial valvulectomy, or conduits). The choice of surgical procedure depends to some degree on the presence and degree of
subvalvular muscular hypertrophy. Palliative therapy with oral medications such as diuretics and vasodilators should be initiated if right-sided CHF is present. The prognosis is typically poor if atrial fibrillation or right-sided CHF is present. If atrial fibrillation is noted, use of a digitalis glycoside may be warranted. |
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